package cn.edu.njust.alg.jisuanke;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		if (n < 2) {
			System.out.println(n);
			sc.close();
			return;
		}
		int[] f = new int[n + 1];
		f[0] = f[1] = 1;
		for (int i = 2; i <= n; i++) {
			f[i] = f[i - 1] + f[i - 2];
		}
		System.out.println(f[n]);
		sc.close();
	}
}